Typical coaxial transmission lines include a length of coaxial cable having a cable connector at each end. The cable connectors enable the coaxial transmission line to be connected to various devices, such that the connected devices are able to communicate with one another by transmitting signals and information through the transmission lines.
Many factors affect coaxial transmission line design, such as performance requirements, cable flexibility and material cost. For example, higher quality coaxial transmission lines employ coaxial cable having a solid outer conductor, which provides for improved performance when compared to coaxial cable having other types of outer conductors such as metallic braiding or foil. Solid outer conductors may take various forms, such as smooth or corrugated, wherein corrugated outer conductors are typically preferred because they provide increased cable flexibility when compared to smooth outer conductors. Additionally, corrugated outer conductors may vary in design, some having annular corrugations and others having helical corrugations.
Cable connectors, which allow the coaxial transmission lines to be connected to devices, are typically interfaced with coaxial cables having solid corrugated outer conductors by soldering the connectors to the outer conductors. For example, brass connectors may be soldered to copper or silver outer conductors, producing high quality coaxial transmission cables. Soldering provides for a strong junction between the outer surface and the cable connector, which results in good intermodulation performance, i.e. minimal noise entering the system due to spurious signals. However, while soldering is an adequate method for interfacing some types of solid outer conductors with cable connectors, the flux used to solder the connection is more corrosive to other metals, such as aluminum. This corrosion decreases conductivity in the coaxial transmission line, which decreases intermodulation performance. The decrease is compounded because the flux used in soldering is also very difficult to remove from the assembled cable conductor interface. Therefore, soldering cable connectors to coaxial cables with aluminum outer conductors results in lower quality cables due to the decreased conductivity in the cables, which reduces cable performance and causes cable failure.
Another cause of decreased coaxial cable performance is galvanic corrosion in the cable connector interface, which results from moisture that is able to penetrate the interface and bridge between the outer conductor and the cable connector. Aluminum outer conductors are also more prone to galvanic corrosion than outer conductors made of other metals, such as copper or silver. Galvanic corrosion is also more prevalent in coaxial cables with helical corrugations than annular corrugations because the helical corrugations provide a path for moisture to enter the interface. Thus, as moisture penetrates the cable connector interface and weakens the junction between the outer surface and the cable connector, intermodulation performance further decreases.
In addition to performance considerations of various coaxial transmission line materials, the market cost of materials must also be considered as a factor in the design of coaxial transmission lines. Therefore, there is a need to provide high quality coaxial transmission lines from more materials, including coaxial cables having aluminum outer conductors by overcoming the deficiencies of the prior art.